if there is resonance, yes. You have to show that you know there are 3 different structures for the same molecule. if you only draw one, one could assume you believe one bond is shorter than the others

I believe we should draw all resonance structures for molecules to show our understanding that lewis structures can have multiple bonds on different equivalent locations and that the actual molecule is a blend or average of all resonance structures.

My TA said that sometimes the problem won't ask you to draw all of the possible resonance structures even if there are multiple resonance structures. This is because (1) they might not want to give away the fact that there are resonance structures in the specific problem or (2) they aren't asking for them. Either way, you should draw all the resonance structures and indicate them with double-sided arrows.

you should draw all of the resonance structures as the true structure will be an average of them all (so by drawing all of them, you show that you know that it can be any of the structures, but is an average in reality)